1. Field of the Invention
This invention relates to a data communicating apparatus for and a data communicating method of transmitting a plurality of data by serial communication.
2. Related Background Art
In various machines, the exchange of data is effected between apparatuses present in the interior of the machine, and with the tendency toward a larger scale of the machines, the quantity of data to be treated is also in a tendency toward increase. When data are on one and the same substrate, it is also possible to effect the exchange of the data by an ordinary bus form. However, when the exchange of data in the bus form is to be effected by using bundle lines or the like between discrete substrates, the number of the bundle lines becomes enormous. At a location which does not require a high data transfer speed, there is known a method of curtailing the number of bundle lines by means of serial exchange of data.
As serial communications, there exist various systems such as the clock synchronizing type communication for effecting communication while adding a serial transfer clock, and non-synchronizing communication which does not add a clock. The communication system which does not add a clock has the great advantage that it can decrease the number of bundle lines. In contrast, in the clock synchronizing type communication, a circuit such as a synchronizing circuit is not necessary on the receiving side and therefore, the circuit construction becomes simple, and this leads to the advantage that the whole can be constructed inexpensively. Also, in an apparatus such as a copying machine or a printer, a stepping motor therein is supplied with a driving pulse at each predetermined time interval to thereby control the rotation of the motor. So, by making design such that serial data are received at a predetermined cycle, it becomes possible to rotate the stepping motor in serial communication without making the scale of the circuit large.
(Example of the Conventional Serial Communication)
Here, an example of the conventional serial communication will be described with reference to FIGS. 7 to 12A and 12B of the accompanying drawings.
FIG. 7 shows the internal circuit of a conventional transmitting unit 200. The control of the transmitting unit 200 is effected by a control CPU 201. The CPU has connected thereto a ROM memory 202 as a program storing device and a RAM memory 203. S-CLOCK as a communication clock signal is supplied by a CLOCK 207, and several circuits in the transmitting unit 200 operate in synchronism with the clock from the CLOCK 207. A parallel/serial conversion circuit 206 exists in order to generate S-DATA as a serial data signal. The data to this converter is supplied from the CPU through a latch circuit 204. At a point of time whereat the CPU has determined to start communication, the loading of the data to the parallel/serial conversion circuit is effected. Actually, a signal (hereinafter referred to as the transmission starting original signal) which is generated from the port of the CPU, and synchronized with the clock from the CLOCK 207 in a SYNC circuit 208 is used to start the loading.
As shown in FIG. 8, the SYNC circuit 208 is a timing circuit for detecting a falling edge of the signal inputted through an input portion In, and generating an “L” signal of one clock synchronized with an inputted clock signal. S-LATCH* as a reception timing signal is generated by a down counter circuit 209. The start of down count, like the parallel/serial conversion circuit 206, is synchronized with the output of the SYNC circuit 208. The internal delay number (the delay of clock up to a data latch portion) of a receiving unit 102, which will be described later, is added to the effective bit number of serial communication data set by the latch circuit 204 and the sum is set as the load value of down count from the CPU through a latch circuit 205. Thereby, the reception decision timing on the receiving unit 400 side of FIG. 9 can be changed, and even when the circuit of the receiving unit is changed, the change can be easily coped with.
FIG. 9 shows the internal circuit of the receiving unit 400. In synchronizing type communication, a clock is also transferred at the same time and therefore, in reception, an inherent clock is not particularly required. In the receiving unit 400, there exist a serial/parallel conversion circuit 402 for converting serial data into parallel data, and a latch circuit 403 for latching the parallel data. S-DATA is transmitted in synchronism with the rising edge of S-CLOCK and therefore, on the receiving unit 400 side, the inputted S-CLOCK is inverted by an inverting circuit 401 and is used as an operating clock in the serial/parallel conversion circuit 402. As a result, the S-CLOCK is received at the falling edge thereof, whereby the degree of supefluity to the delay of transmission by a communication line is increased. The latch circuit 403 is adapted to decide (or latch) the parallel data from the serial/parallel conversion circuit 402 at the rising of S-LATCH*.
FIG. 10 shows an example of the communication when use is made of the transmitting unit 200 of FIG. 7 and the receiving unit 400 of FIG. 9. Here, the effective bit number of communication data is 8 bits, and data to be transmitted is defined as D1[7:0], and data already decided on the receiving unit 400 side is defined as D0[7:0]. In synchronism with the rising of S-CLOCK, the data D1 is transmitted sequentially from 0 bit. LSB first or MSB first may be either. The circuit in the serial/parallel conversion circuit 402 in the receiving unit 400 only changes. As soon as the data D1[7] of the 8th bit is transferred, S-LATCH* becomes “L” by one clock. In the receiving circuit shown in FIG. 9, this becomes simultaneous with D1[7] because the internal delay does not occur. In synchronism with the rising of S-LATCH*, the data is changed from D0[7:0] to D1[7:0]. The change timing of the data depends on S-LATCH*. This S-LATCH* is outputted from the port output of the CPU 201 with shifting by a predetermined time corresponding to a down count value set by the down counter 209. As a result, design is made such that if the CPU generates the transmission starting original signal (reception timing signal) at each predetermined timing, data output can be renewed also at each predetermined timing.
Generally, in serial communication, the more increased is the amount of data transmitted, the longer becomes the communication time. To suppress such a problem, the transfer speed (in the case of the clock synchronizing type communication, the transfer clock frequency) of communication is increased and the time required for the transfer is suppressed to a short time. However, in the clock synchronizing type communication wherein a clock signal is transmitted via a bundle line, an increase in the frequency of the transfer clock leads to the aggravation of radiant electric wave noise. As a method of suppressing the radiant electric wave (or EMI) occurring from a clock, there is known a noise countermeasure technique using an SSCG (spread spectrum clock generator). This technique generates a clock while modulating a frequency at a constant width, and is a technique very effective when no problem is posed in the case of the modulation of a minute sectional width.
FIG. 11 shows the main body construction of a conventional digital composite machine, and the above-noted problem will hereinafter be described in detail with respect to a digital copying machine as an image forming apparatus taken as an example. An original transporting portion 130 is constructed as follows. Originals set on an original placing stand 131 are transported one by one to an original reading position by feed rollers 132. In the original reading position, the original is disposed at a predetermined position by an original transporting belt 137 driven by a motor 136 and the original reading operation is performed by an original reading portion 120. After the original reading operation, the transporting path is changed by a flapper 135, and the motor 136 is reversed in rotation, whereby the original is delivered to a delivery tray 138.
An original reading portion 120 is constructed as follows. An exposure lamp 122 comprises a fluorescent lamp, a halogen lamp or the like, and irradiates the original on an original supporting glass plate (original stand) 126 while moving in a direction perpendicular to the lengthwise direction thereof. The scattered light from the original by the irradiation by the exposure lamp 122 is reflected by first and second mirror stands 121 and 123 and arrives at a lens 124. At this time, the second mirror stand 123 is moved at a speed of ½ relative to the movement of the first mirror stand 121, and the distance from the irradiated original surface to the lens 124 is always kept constant. The first mirror stand 121 and the second mirror stand 123 are moved by a reading motor 125. The image on the original is imaged on the light receiving portion of a CCD line sensor 127 comprising thousands of light receiving elements line-arranged, through the intermediary of the mirror stands 121, 123 and the lens 124, and is sequentially photoelectrically converted in units of line by the CCD line sensor 127. The photoelectrically converted signal is processed by a signal processing portion, not shown, and is PWM-modulated and outputted.
An image forming portion 100 is constructed as follows. An exposure control portion drives a semiconductor laser 50 on the basis of a PWM-modulated image signal which is the output of the signal processing portion, and applies a light beam to the surface of a photosensitive member 52 being rotated at a constant speed. At this time, the light beam is deflected and scanned by the use of a polygon mirror 51 being rotated in parallel to the axial direction of the drum-shaped photosensitive member 52 by a motor 54. The photosensitive member 52, before the light beam is applied thereto, has its residual charges eliminated by a pre-exposure lamp, not shown, and has its surface uniformly charged by a primary charger, not shown. Accordingly, the photosensitive member 52 receives the light beam while being rotated, whereby an electrostatic latent image is formed on the surface of the drum. The electrostatic latent image on the surface of the drum is then visualized with a developer (toner) of a predetermined color by a developing device 53.
Transfer paper transported from a transfer paper feeding stage 140, 150, 160, 170 or 180 is transported to registration rollers 55. The registration rollers 55 detects the arrival of the transfer paper by the use of a sensor 56, and feeds the transfer paper to a transferring position while watching the timing between the leading edge of the image formed on the photosensitive member 52 and the leading edge of the transfer paper. The reference numeral 57 designates a transfer charger which transfers the developed toner image on the photosensitive member 52 to the fed transfer paper. After the transfer, the photosensitive member 52 has any residual toner thereon removed by a cleaner, not shown. The transfer paper after the transfer of the image thereto has been finished is easy to separate from the photosensitive member 52 because the curvature of the photosensitive member 52 is great, but a voltage is applied to a charge eliminating needle, not shown, to thereby weaken the attraction between the photosensitive member 52 and the transfer paper and facilitate the separation.
The thus separated transfer paper is sent to a fixing portion 58, where toner thereon is fixed. The reference numeral 110 denotes a ceramic heater comprised of film 111 and two rollers, and the heat of the ceramic heater 110 is efficiently transmitted through the thin film 111. A cooling roller radiates the heat of the rollers of the fixing portion. A feed roller is comprised of a large roller and two small rollers, and feeds the transfer paper from the fixing portion and also corrects the curl of the transfer paper.
A direction flapper 112 changes over the destination of delivery of the transfer paper between a tray 114 and a transporting unit 190 in conformity with the operating mode.
The transporting unit 190 is constructed as follows. This is a unit for transporting the transfer paper to a post-treating apparatus 10 which will be described later, and transports the transfer paper by transport rollers 191. The reference numerals 140, 150, 160 and 170 designate main body feeding stages comprised of the same mechanism. The reference numeral 180 denotes a deck feeding stage which can accumulate thereon a larger quantity of transfer paper than the main body feeding stages 140, 150, 160 and 170. The main body feeding stages 140, 150, 160 and 170 assume substantially the same construction and therefore, the construction of the main body feeding stage 140 will be taken as an example and described. On the bottom surface of a cassette 141 for accumulating and containing the transfer paper therein, there is disposed a bottom plate 142 moved up and down by a lift-up motor 143. This bottom plate 142 is moved up, whereby the transfer paper can stand by at a predetermined standby height. The transfer paper standing by at a predetermined position is transported to a pair of feed rollers 145 by the use of a pick-up roller 144. The pair of feed rollers 145 have torque applied thereto in a rotational direction opposite to the feeding direction, thereby feeding the transfer paper to a transport path one by one while preventing the double feeding of the recording mediums. Also, the pair of transport rollers 146 are a pair of rollers for further upwardly transporting the transfer paper transported from the feeding stages underlying the main body feeding stage 140. A feed motor 147 is a motor for driving the pair of feed rollers 145 and the pair of transport rollers 146.
The deck feeding stage 180 is constructed as follows. Also on the bottom surface of a paper container 181 for accumulating and containing the transfer paper therein, there is disposed a bottom plate 182 for moving up the transfer paper to the standby position. The bottom plate 182 is connected to a belt rotated by a motor 183, and by the belt being moved, the upward movement and downward movement of the bottom plate 182 are controlled. The transfer paper being at the standby position is transported to a pair of feed rollers 184 by a pick-up roller 185, and as in the case of the main body feeding, the transfer paper is transported to a transport path while the doubling feeding thereof is prevented. A feed motor 187 is a motor for driving the pair of feed rollers 184.
The post-treating apparatus 10 is constructed as follows. The post-treating apparatus 10 receives the transfer paper from the image forming portion 100 by rollers 32. When a tray 14 is selected as the output destination of the received transfer paper, the transport direction is changed over by a flapper 33 and the transfer paper is delivered to the tray 14 by the use of rollers 34. The tray 14 is a delivery tray temporarily used as the destination of delivery in the treatment effected while interrupting the ordinary processing.
A tray 18 and a tray 19 are trays for ordinary delivery. The transfer paper can be delivered to these trays by the transport path being downwardly changed over by the flapper 33, and thereafter the transport path being selected toward rollers 16 by a flapper 30. When the transport path is vertically downwardly selected by flappers 30 and 31 and the transport direction is reversed by reversing rollers 15, reverse delivery is possible. During the delivery to these trays 18 and 19, stapling using a stapler 17 is possible. Also, the selection of the tray 18 or the tray 19 as the output destination of the transfer paper is effected by moving up and down the tray itself by the use of a shift motor 20.
A tray 27 is a delivery tray for use during binding. The transfer paper is transported from the rollers 15 to rollers 21 and a predetermined quantity of transfer papers are accumulated in a primary accumulating portion 23. After the termination of the accumulation, binding work is done by a stapler 24, and the direction of a flapper 25 is changed and rollers 22 are rotated in a direction opposite to that during the accumulation, and the transfer paper is delivered to the tray 27 via rollers 26.
When the simplification of an interface is taken into consideration when the image forming portion 100, the original reading portion 120, the main body feeding stage 140, etc. and the deck feeding stage 180 are designed to be separable from each other, the connecting method by serial communication is general. In this case, various motors, e.g. the reading motor 125 and the feed motor 147 are controlled by serial communication from a control device, not shown, in the image forming apparatus 100.
Also, when as described above, the communication clock is subjected to SSCG modulation in order to reduce radiation noise, if each motor has a control device attached thereto (for example, a DC brushless outer rotor motor), no problem will arise regarding the driving accuracy thereof, but in the case of stepping motors often used in recent years, there are problems which must be considered regarding accuracy.
FIGS. 12A and 12B show the changeover of the excitation pattern of a stepping motor in synchronizing type serial communication using S-LATCH*. When SSCG is not used, a communication clock period which is the reference is the same and therefore, the renewal timing of S-LATCH* is constant. As a result, the frequency which is the rotational speed of the stepping motor becomes constant.1/T1=1/T2=1/T3=1/T4
When SSCG is used, the communication clock which is the reference fluctuates and therefore, the renewal timing of S-LATCH* becomes irregular. As a result, the frequency of the stepping motor varies irregularly.1/T1≠1/T2≠1/T3≠1/T4:  state expression I1/T3<1/T2<1/T1<1/T4:  state expression II
The following two problems are mentioned as the problems when SSCG is used for the driving of the stepping motor of the digital composite machine of FIG. 11.
(1) Deterioration of the Image
The reading of an image is effected at a predetermined magnification by the reading motor 125 driving the first and second mirror stands 121 and 123 at a constant speed. In the contrary to this condition, when the speed is not constant in case of the state expression I as shown in FIG. 12B, the image read becomes a bad image which repeats expansion and contraction.
(2) Bad Paper Transport (Bad Motor Driving)
High torque is required of the feed motor 147 and therefore, there are many cases where the operating frequency and the step-out frequency have no surplus. If in such cases, the speed varies as in the state expression II, the step-out frequency will be exceeded at 1/T4, and there will come out the possibility of the motor being de-coupled and stopped. To avoid this, great limitations will come out in the frequency range of SSCG, the selection of the torque of the motor, etc.